Aquaculture, the farming of aquatic organisms like fish, mollusks, and crustaceans, is the fastest-growing food production sector globally. This growth is driven by increasing worldwide demand for protein and the stagnation of wild-capture fisheries. By 2020, aquaculture production surpassed wild catches as the primary source of seafood for human consumption. The industry’s sustainable expansion depends heavily on the nutritional diets provided to farmed species. These manufactured feeds are the largest operating cost for farmers and the greatest determinant of the industry’s environmental footprint, dictating performance from marine ecosystem health to greenhouse gas emissions.
Core Components and Resource Dependency
Modern aquaculture feed formulations are complex, relying on diverse protein and lipid sources to meet the specific needs of farmed species. Traditionally, the diets of carnivorous fish like salmon and trout contained high proportions of Fishmeal (FM) and Fish Oil (FO). These marine ingredients are derived from reduction fisheries, which harvest small, wild-caught forage fish like anchovies, sardines, and herring.
The industry has progressively lowered its reliance on these finite marine resources over the past two decades. This reduction has been achieved by replacing a significant portion of FM and FO with terrestrial alternatives. Plant proteins, such as soy, corn gluten, and rapeseed meal, now constitute a large fraction of many aquafeeds. However, the use of marine ingredients remains necessary, especially for the Omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) found in fish oil.
The industry’s reliance on wild fish is quantified using the Forage Fish Dependency Ratio (FFDR). This metric calculates the weight of wild forage fish required to produce one unit of farmed fish, excluding marine ingredients sourced from processing by-products. Due to efficiency gains and ingredient substitution, the global FFDR has improved substantially, dropping to approximately 0.13 to 0.19 kg of wild fish needed per kilogram of farmed fish in 2020. Despite this improvement, the aquaculture sector still consumes a substantial share of the global FM and FO supply, historically using between 70% and 78% of the world’s fishmeal and around 68% of the fish oil.
Ecological Footprint of Ingredient Sourcing
The sourcing of traditional feed ingredients creates significant ecological pressure, both in marine and terrestrial environments. Reduction fisheries targeting forage fish stocks can disrupt the marine food web, as these small pelagic species serve as a foundational prey source for larger wild fish, seabirds, and marine mammals. High fishing rates on these stocks can amplify natural population fluctuations, potentially leading to ecosystem-wide consequences.
The diversion of large volumes of forage fish to feed production also raises food security concerns. In many developing coastal nations, these small fish are a locally available and affordable source of protein and micronutrients for human consumption. When these fish are processed into feed ingredients for aquaculture products destined primarily for developed markets, local fresh fish prices can inflate. This transfer of protein from low-income consumers to high-income consumers is a significant ethical consideration.
The shift to plant-based ingredients introduces a different set of environmental challenges related to land use. Soy protein is the most widely used plant protein in aquafeeds, but its large-scale cultivation is a major driver of global deforestation and land conversion. The environmental impact is particularly pronounced when soy is sourced from regions associated with high deforestation risk, such as the Amazon and Cerrado biomes in South America.
The carbon footprint of plant-based ingredients is heavily influenced by how and where they are grown. Land Use Change (LUC), which includes deforestation, can add between 1.2 and 1.6 kilograms of CO2-equivalent emissions for every kilogram of soy meal produced. For example, switching from standard Brazilian-sourced soy protein concentrate to a certified, low-deforestation alternative can reduce the carbon footprint by a factor of more than four.
Novel Ingredients for Sustainable Aquaculture
To further decouple aquaculture growth from traditional resource constraints, research is focused on developing novel and low-impact ingredients. Single-Cell Proteins (SCP), derived from the fermentation of microorganisms such as yeast, bacteria, and fungi, represent a promising alternative. SCP production is highly efficient, yielding protein-rich biomass (up to 70% protein content) with a balanced amino acid profile suitable for fish diets. SCP production can be operated year-round, is independent of weather conditions, and requires minimal arable land or freshwater, offering substantial resource advantages over traditional crops.
Algae and microalgae are being developed specifically to solve the Omega-3 problem posed by reducing fish oil inclusion. These microscopic plants are the original source of EPA and DHA in the marine food web. Cultivating microalgae allows for the direct production of these essential fatty acids in a controlled environment, providing a direct replacement for fish oil without relying on forage fish.
Insect-based proteins, primarily from species like black soldier fly larvae, are also emerging as a viable alternative protein source. These larvae can be reared on various organic side streams and industrial byproducts, embodying a circular economy model by converting waste into high-quality animal feed. However, the adoption of novel ingredients faces significant hurdles, including high production costs and regulatory complexity.
The cost of insect meal, for instance, remains uncompetitive, with prices estimated to be several times higher than both fishmeal and soy meal. Regulatory frameworks, particularly in regions like the European Union, impose restrictions on which waste streams can be used to feed the insects due to food safety concerns. This limits the ingredients’ potential to operate entirely on industrial waste and achieve the scale required to transform the global aquafeed industry.
Water Quality and Waste Management Impacts
While ingredient sourcing affects upstream ecosystems, the use of feed also generates downstream environmental impacts at the farm site itself. Not all feed is consumed by the farmed fish, and metabolic processes result in the excretion of organic waste. This uneaten feed and fish feces are the primary sources of excess nutrients, including dissolved nitrogen and phosphorus, that enter the surrounding water body.
In high-density farming operations, this nutrient discharge can exceed the natural capacity of the local ecosystem to assimilate the waste. The resulting nutrient loading can lead to eutrophication, a process where excessive growth of algae is triggered, which subsequently reduces dissolved oxygen levels when the algae decompose. These localized oxygen depletions can harm or displace native aquatic life.
A significant portion of the solid waste falls to the seabed, causing organic enrichment of the benthic habitats directly beneath the net pens. This accumulation of organic matter stimulates microbial activity, which consumes oxygen and can lead to anoxic, or zero-oxygen, conditions in the sediment. Sediment sulfide concentration is a common indicator used to monitor this impact, with levels above 6,000 micromoles indicating severe damage to the marine habitat.
Feed management strategies are employed to mitigate these downstream effects. Precision feeding techniques, which use acoustic sensors and cameras to monitor fish appetite, reduce the amount of uneaten feed sinking to the bottom. Siting farms in well-flushed areas, where currents can disperse the waste, is another important management practice. When impacts are detected, practices like fallowing—temporarily moving the pens to allow the seabed to recover naturally—are implemented to restore the benthic environment.